Woofer

The name is from the onomatopoeic English word for a dog's deep bark, "woof"[1] (in contrast to a tweeter, the name used for loudspeakers designed to reproduce high-frequency sounds, deriving from the shrill calls of birds, "tweets").

The most common design for a woofer is the electrodynamic driver, which typically uses a stiff paper cone, driven by a voice coil surrounded by a magnetic field.

This approach presents difficulties as not all distortion can be eliminated using servo techniques, and a poorly designed enclosure can swamp the benefits from any attempt at electronic correction.

Because the characteristics of a loudspeaker can be measured, and to a considerable extent predicted, it is possible to design special circuitry that somewhat compensates for the deficiencies of a speaker system.

By using finite impulse response (FIR) and other digital techniques, the crossovers for a bi-amped or tri-amped system can be accomplished with a precision not possible with analog filters, whether passive or active.

The three chief properties designers look for in cones are light weight, stiffness, and lack of coloration (due to absence of ringing).

The disadvantage of this type of frame is that the basket may flex if the speaker is driven at high volumes, there being resistance to bending only in certain directions.

Cast baskets are more expensive, but are usually more rigid in all directions, have better damping (reducing their own resonance), can have more intricate shapes, and are therefore usually preferred for higher quality drivers.

Further heating can physically distort the voice coil, causing scuffing, shorting due to wire insulation deterioration, or other electrical or mechanical damage.

Sudden impulse energy can melt a section of voice coil wire, causing an open circuit and a dead woofer; the necessary level will vary with driver characteristics.

In normal listening level music applications, the electrical power rating of woofers is generally unimportant; it remains important for higher frequency drivers.

Some drivers include provisions for better cooling (e.g., vented magnet pole pieces, dedicated heat conduction structures) to reduce increased coil/magnet/frame temperatures during operation, especially high power level conditions.

If too much power is applied to the voice coil as compared to its ability to shed heat, it will eventually exceed a maximum safe temperature.

The trade-off for high efficiency at reasonable cost is usually relatively low excursion capability (i.e., inability to move "in and out" as far as many home woofers can), as they are intended for horn or large reflex enclosures.

The larger the room, the more air the woofer's movement will have to displace in order to produce the required sound power at low frequencies.